depends upon what you want to do ! This question comes up almost daily and it's difficult to answer without any info on what someone wants to machine or what they expect to spend .
If you want pro software then I'm all over mastercam , It's easy to use , I use it regularly and I haven't come across much if anything that I couldn't accomplish with it , but it comes with a heavy price tag
if your only planning on simple shapes and drilling holes then the most economical is to hand code .
As was mentioned above both softwares are cheap and functional , personally I'd lean more toward cambam .
Another cheap software if your more into surfacing and 3d stuff is the notorious bobcad , Quite often v23 comes up on ebay and it can be fairly cheap , it's an older version but in my opinion crashes far less than their newer version ( save button is a guys friend) . The newer version does have more 3d features which work pretty well and the code is safe most of the time , the 2d sucks
A poet knows no boundary yet he is bound to the boundaries of ones own mind !! ........